Switching acidity on manganese oxide catalyst with acetylacetones for selectivity-tunable amines oxidation

Xiuquan Jia,Jie Xu,Jin Gao,Fei Xia,Jiping Ma,Mingxia Gao

doi:10.1038/s41467-019-10315-9

Abstract

The design of metal oxide catalysts predominantly focuses on the composition or geometry engineering to enable optimized reactivity on the surface. Despite the numerous reports investigating the surface chemisorption of organic molecules on metal oxides, insights into how adsorption of organic modifiers can be exploited to optimize the catalytic properties of metal oxides are lacking. Herein, we describe the use of enolic acetylacetones to modify the surface Lewis acid properties of manganese oxide catalysts. The acetylacetone modification is stable under the reaction conditions and strongly influences the redox-acid cooperative catalysis of manganese oxides. This enables a rational control of the oxidation selectivity of structurally diverse arylmethyl amines to become switchable from nitriles to imines.

Highlights

The design of metal oxide catalysts predominantly focuses on the composition or geometry engineering to enable optimized reactivity on the surface
Much less is known about the study on tuning the selectivity of metal oxide catalyst via organic modification[22,23], metal oxides are used in various fields of bifunctional catalysis as a result of their acid–base and redox properties with high thermal stability and durability[24,25,26,27,28]
After pre-adsorption of acac on manganese oxides (MnOx), the band at 1440 cm−1 was scarcely observed under identical conditions. These results demonstrate that the Lewis acidic sites on the surface of MnOx can be blocked by preadsorption of acac modifier

Summary

Introduction

The design of metal oxide catalysts predominantly focuses on the composition or geometry engineering to enable optimized reactivity on the surface. The acetylacetone modification is stable under the reaction conditions and strongly influences the redox-acid cooperative catalysis of manganese oxides. This enables a rational control of the oxidation selectivity of structurally diverse arylmethyl amines to become switchable from nitriles to imines. We have made such catalysts by employing amorphous MnOx as redox-acid cooperative catalyst for the double dehydrogenation of primary amines to nitriles, and the acetylacetone (acac) modifier switches the selectivity from nitriles to imines by selectively suppressing the Lewis acidic sites on MnOx catalyst. This work provides an opportunity for using manganese oxide catalyst for the synthesis of both imines and nitriles in high selectivity from primary amines via aerobic oxidation, and contributes an example of regulating the catalytic selectivity of metal oxide catalysts by organic modification on the surface

Methods

Results

Conclusion